When drilling a well, a borehole is typically drilled from the earth's surface to a selected depth and a string of casing is suspended and then cemented in place within the borehole. A drill bit is then passed through the initial cased borehole and is used to drill a smaller diameter borehole to an even greater depth. A smaller diameter casing is then suspended and cemented in place within the new borehole. This is repeated until a plurality of concentric casings are suspended and cemented within the well to a depth which causes the well to extend through one or more hydrocarbon producing formations.
Rather than suspending a concentric casing from the bottom of the borehole to the surface, a liner is often suspended adjacent to the lower end of the previously suspended casing, or from a previously suspended and cemented liner, so as to extend the liner from the previously set casing or liner to the bottom of the new borehole. A liner is defined as casing that is not run to the surface. A liner hanger is used to suspend the liner within the lower end of the previously set casing or liner.
A running and setting tool disposed on the lower end of a work string may be releasably connected to the liner hanger, which is attached to the top of the liner. The work string lowers the liner hanger and liner into the open borehole until the liner hanger is adjacent the lower end of the previously set casing or liner, with the lower end of the liner typically slightly above the bottom of the open borehole. When the liner reaches the desired location relative to the bottom of the open borehole and the previously set casing or liner, a setting mechanism is conventionally actuated to move an anchoring element (e.g., slips) on the liner hanger from a compressed position to an expanded position and into engagement with the previously set casing or liner. Thereafter, when a downward force is applied to the anchoring body, the anchoring element is deployed to set and support the liner.
The liner hanger anchoring element can include a radially expandable and contractable c-ring with slip teeth formed about its outer and inner edge and a frustoconical tapered surface for supporting the liner within the previously set casing or liner. Typically, the c-ring slip (or anchoring body) is held in a compressed position within a recess in the body of the liner hanger while the liner hanger is lowered through the borehole. The c-ring slip is then moved out of the recess in the body of the liner hanger, and into its expanded position.
Unfortunately, the c-ring slip can sometimes become dislodged from the recess in the liner hanger body while the liner hanger is being lowered through the borehole, thereby unintentionally expanding the anchoring element before the liner hanger is ready to be set. This premature expansion of the anchoring element can cause undesirable delays, since the liner hanger assembly must be removed from the wellbore and the anchoring element reset.